Are you suggesting by this line of thinking that the soul is an inheritable trait like a big brain or something else?
Naturally, we're deep into the realm of speculation at this point, but we have souls because the first man was given a soul, and it thereby became a trait of his offspring and descendents thereafter. How that occurs in each case, I won't speculate. Shall we call it a mystery? Or would you like to propose an answer?
PS In a sense, Eve, too, was one of Adam's descendents, as she came from him.
